Although anastrozole (Anas) plays a key role in the management of endocrine sensitive post-menopausal (PM) breast cancer (BC), there is much variability in its efficacy and tolerability. Anas-associated musculoskeletal symptoms (MS) and other adverse reactions, such as hot flashes (HF) and vaginal dryness/dyspareunia (VDD), are common and can affect the quality of life of BC patients, even sometimes leading to treatment withdrawal. The aim of this study was to determine the clinical and demographic factors associated with these adverse events. This is a cross-sectional study in estrogen receptor (ER) positive PM women (n = 92) with stages I to III BC receiving Anas. Multivariate analyses were performed to investigate the factors associated with Anas-induced adverse effects such as MS, HF and VDD. A serum estradiol concentration was undetectable (< 36.7 pmol/L) in 68.1% of patients but was detectable within a normal range (>36.7-88.1 pmol/L) in the other 31.9% of patients, and this group was found to have a lower odds of having at least one adverse effect (AE) compared to those with undetectable levels [adjusted odds ratio (AOR) 0.12, 95% confidence interval (CI) 0.02 to 0.64, p = 0.013]. Women with grades II and III tumors and a family history of BC had a higher odds of AE (grade II: AOR 12.22, CI 1.48 to 100.80, p = 0.020; grade III: AOR 12.95, CI 1.25 to 134.33, p = 0.032) and VDD (AOR 5.99, CI 1.30 to 27.52, p = 0.021), respectively. Patients who received Anas treatment for more than one year had a higher odds of VDD (one to three years: AOR 34.57, CI 3.86, 309.50, p = 0.002; more than 3 years: AOR 27.90, CI 2.21 to 351.84, p = 0.010). Advanced age also lowered the odds of HF (AOR 0.90, CI 0.83 to 1.00, p = 0.049). In conclusion, patients' hormonal environments and durations of Anas treatment may play a role in developing Anas-induced adverse effects.